Gear drive for electrophotographic printing machine

ABSTRACT

An apparatus in which a pair of gear members include alternate resilient and rigid portions producing flexure in each of the gears so that backlash is minimized.

United States Patent 1191 I Hawley 1 Oct. 29, 1974 GEAR DRIVE FOR3,361,002 1/1968 Staehlin 74/409 ELECTRQPHOTOGRAPHIC PRINTING 3,406,58310/1968 Baier 74/411 MACHINE D FOREIGN PATENTS OR APPLICATIONS [75]Inventor Charles Hawley Webster 1,319,233 1/1963 France 74/461 [73]Assignee: Xerox Corporation, Stamford,

Conn' Primary Examiner-Leonard I-I. Gerin [22] Filed: June 14, 1973Attorney, Agent, or FirmI-I. Fleischer; C. A. Green; 21 Appl. No.:370,181 Ralabate [52] US. Cl. 741/409 5 ABSTRACT [51] Int. Cl. F16h55/18 1 Field of Search An apparatus in which a pair of gear membersinclude 74/461 alternate resilient and rigid portions producing flexurein each of the gears so that backlash is minimized.

[56] References Cited 8 Claims, 3 Drawing Figures summit PATENTEU "CT 29I974 GEAR DRIVE FOR ELECTROPHOTOGRAPHIC PRINTING MACHINE The foregoingabstract is neither intended to define the invention disclosed in thespecification, nor is it intended to be limiting as to the scope of theinvention in any way.

BACKGROUND OF THE INVENTION shafts which require close tolerancesbetween their center to center distances. This insures that when thegear members mesh with one another backlash therebetween is minimized.Backlash is the amount by which the width of a tooth space exceeds thethickness of the engaging tooth on the pitch circles thereof. In orderto minimize backlash, it is frequently necessary to specify the distancebetween centers of the shaft members extremely precisely. Control of thetolerances between shaft members insures that backlash or relativemovement between gears is minimized. When the shaft members are arrangedto be removed readily from the electrophotographic printing machine itis frequently not feasible to have tightly toleranced distances betweenrespective centerlines. This is particularly true in the case of anelectrophotographic printing machine wherein the photoconductive drumand transfer roll are readily removed therefrom and yet have to rotatein synchronism with'one another. By way of example, in the case ofmulti-color electrophotographic printing a cut sheet of support materialis secured to the transfer roll for recirculation thereon. Successivesingle color toner powder images are transferred to the cut sheet ofsupport material from the photoconductive drum. The photoconductive drumand the transferroll rotate at substantially the same angular velocityenabling successive toner powder images to be superimposed inregistration with one another on the sheet of support material. A commondrive motor rotates the photoconductive drum and transfer roll through agearing arrangement. It has been found that it is highly desirable tominimize backlash between the gears driving both the photoconductivedrum and the transfer roll to prevent relative movement therebetween.Relative movement between the photoconductive drum and transfer roll mayproduce errors in registration between successive toner powder images.In' the past, relative movement has been controlled by preciselytolerancing the center to center-distance between the photoconductivedrum shaft and the transfer roll shaft. Finally, the respective gears onthe heretofore mentioned shafts are precisely machined to minimizebacklash therebetweemln fact, frequently it has been necessary toprovide for an interference fit between the respective gears to reducerelative movement therebetween, i.e. backlash.

It has been found that in order to produce a satisfactory multi-colorimage of any original document, it isnecessary to superimpose successivesingle color toner powder images on one another in registration. Hence,this requires exceedingly close tolerancesbetween the respective shaftmembers to minimize backlash between the respective gears. However, itis also highly desirable to remove the photoconductive drum and transferroll readily from the printing machine in order to simplify themaintenance thereof. The foregoing objectives conflict with one anotherin that the requirement for a tightly toleranced center to centerdistance between the shaft members may prevent the ready removal of thephotoconductive drum and transfer roll from the printing machine.

Accordingly, it is aprimary object of the present invention to improvemeshing gear members so that backlash therebetween is minimized whilemaximizing the permissible shaft to shaft centerline tolerance.

SUMMARY OF THE INVENTION Briefly stated, and in accordance withthepresent invention, there is provided an apparatus rotating a firstshaft member at a substantially predetermined angular velocity relativetoa second shaft member with substantially no relative movementtherebetween.

In the present instance, the apparatus includes a first gear membermounted on the first shaft member and a second gear member mounted onthe second shaft members. Preferably, the first gear member includes aplurality of resilient portions equally spaced between rigid portionsthereof. The resilient portions are disposed at substantially about apreselected radius on the first gear member. Similarly, the second gearmember includes a plurality of resilient portions equally spaced betweenrigid portions thereof. In like manner, the resilierit portions arelocated at substantially about a preselected radius on the second gearmember. The first gear member meshes with the second gear member in acontact zone such that the shaft members rotate at the predeterminedangular velocity with substantially no relative movement therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of thepresent invention will become apparent upon reading the followingdetailed description and upon reference to the drawings, in which:

FIG. 1 schematically illustrates an electrophotographic printing machineembodying therein the features of the present invention;

FIG. 2 is a perspective view showing the gearing arrangement of the FIG.1 printing machine; and

FIG. 3 is an elevational view depicting one of the FIG. 2 gears.

While the present invention will be described in connection with apreferred embodiment, it will be understood that it is not intended tolimit the invention to that embodiment. On the contrary, it is intendedto cover all alternatives, modifications and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims.

DETAILED DESCRIPTION OF THE INVENTION 7 For a general understanding ofthe disclosed multicolor electrophotographic printing machine in'whichthe present invention may be incorporated, continued reference is had tothe drawings. In the drawings, like reference numerals have been usedthroughout to designate like elements. Turning now to FIG. 1, thevarious components of the multi-color printing machine are illustratedschematically therein. Although the gearing arrangement of the presentinvention is particularly well adapted for use in this type of anelectrophotographic printing machine, it should become evident from thefollowing discussion that it is equally well suited for use in a widevariety Qfmachines, and is not necessarily limited to the particularembodiment shown herein. 1

As depicted in FIG. 1, the electrophotographic printing machine employsa drum having a photoconductive surface 12 secured to and entrainedabout the exterior circumferential surface thereof. Drum 10 is mountedrotatably on the machine frame and driven at' a substantially constantangular velocity, in the direction of arrow 14, by drive motor 16 (FIG.2). As drum 10 rotates, photoconductive surface 12 passes sequentiallythrough a series of processing stations. Drive motor I6 rotates drum 10at a predetermined speed (in this case 9.6 revolutions per minute)relative to the other operating mechanisms of the printing machine. U.S.Pat. No. 3,655,377 issued to Sechak in 1972 demagnetic brush developerunits". A typical magnetic scribes a suitable photoconductive surface. Atiming disc (not shown) mounted on one end of the shaft of drum 10cooperates with the machine logic to synchronize the various operationswith the rotation of drum 10. In this way, the proper sequence of eventsis produced at the respective processingstations.

Initially, drum 10 rotates photoconductive surface 12 through chargingstation A. At charging station A, a corona generating device, indicatedgenerally at 18, extends longitudinally in a transverse direction acrossphotoconductive'surface 12. This enables corona generating device 18to'spray ions onto photoconductive surface 12 to produce a relativelyhigh, substantially uniform charge thereon. Preferably, coronagenerating device 18 is of the type described in U.S. Pat. No. 2,778,946issued to Mayo in 1957.

After photoconductivesurface 12 is charged to a substantially uniformpotential, drum 10 is rotated to exposure station B. At exposure stationB, a color filtered light image of original document 20 is projectedonto charged photoconductive surface 12. Exposure station B includes amoving lens system, generally designated by the reference numeral 22 anda color filter mechanism shown generally at 24. A suitable moving lenssystem is disclosed in U.S. Pat. No. 3,062,108 issued to Mayo in I962.Original document 20, such as a sheet of paper, book, or the like isplaced face down upon transparent viewing platen 26. As shown in FIG. I,lamps 28 are adapted to move in a timed relationship with lens 22 andfilter mechanism 24 to scan successive incremental areas of originaldocument 20 disposed upon platen 26. In this manner, a flowing lightimage of original document 20 is projected onto the chargedphotoconductive surface 12. During the exposure process, filtermechanism 24 interposes selected color filters into the optical lightpath of lens 22. The appropriate filter operates on the light raystransmitted through lens 22 to record an electrostatic latent image onphotoconductive surface 12, corresponding to a preselected spectralregion of the electromagneticwave spectrum, hereinafter referred to as asingle color electrostatic latent image.

Drum 10 next rotates to development station C. At development station C,three individual developer units, generally indicated by the referencenumerals 30, 32 and 34, respectively, are arranged to render visible theelectrostatic latent image recorded on photoconductive surface 12.Preferably, each of the developer units are of a type generally referredto in the art as brush developer unit utilizes a magnetizable developermix which has carrier granules and toner particles therein. Generally,the toner particles are heat settable. In operation, the developer mixis continually brought through a directional flux field to form a brushthereof.

The electrostatic latent image recorded on photoconductive surface 12 isbrought into contact with the brush of developer mix. Toner particlesare attracted from the developer mix to the latent image. Each of therespective developer units contain appropriately colored toner particlescorresponding to the complement of the spectral region of the wavelength of light transmitted through filter 24. For example, a colorfiltered electrostatic latent image is developed by depositing greenabsorbing magenta toner particles thereon. Blue and red filtered latentimages are developed vwith yellow and cyan toner particles,respectively.

After development, the now visible toner powder image is advanced totransfer station D. At transfer station D, the toner powder imageadhering electrostatically to photoconductive surface 12 is transferredto a sheet of final support material 36. Final support material 36 maybe, amongstothers, plain paper or a sheet of thermoplastic polysulfonematerial. A transfer roll, shown generally at 38, secures supportmaterial 36 releasably thereto for movement in a recirculating paththerewith. Transfer roll 38 is adapted to rotate in synchronism withdrum 10 (in this case at substantially the same angular velocitytherewith). This is achieved by the gearing arrangement of the presentinvention. Gear member 40 mounted on shaft member 42 of drum l0 drivesgear member 44 mounted on shaft member 46, of transfer roll 38. Thegearing arrangement disclosed in FIG. 1 will be more fully discussedwith reference to FIG. 2. Inasmuch as a plurality of toner powder imagesare transferred from photoconductive surface 12 to support material 36,each image transferred thereto must be superimposed in registration withthe prior one. The relationship of gear 40 to gear 44, i.e. the backlashtherebetween directly affects image registration. Preferably,registration between successive images should not exceed about 0.006inches of misalignment. Image transfer is achieved by .electricallybiasing transfer roll 38 to a potential having sufficient magnitude andthe proper polarity to attract electrostatically toner particles fromthe latent image recorded on photoconductor surface 12 to supportmaterial 36. It should be noted that gear 40 rotates in the direction ofarrow 14 and therebydrives gear 44, which in turn rotates transfer roll38, in the direction of arrow 48. U.S.

align the advancing sheet and move it to transfer roll 38 where gripperfingers 62 secure it thereto. After a plurality of toner powder imageshave been transferred from photoconductive surface 12 to supportmaterial 36, gripper fingers 62 separate support material 36 from thesurfaceof transfer roll 38. This permits stripto be advanced on endlessconveyor 66 to fusing station Continuing now with the description of theformation of a muIti-color copy, at fusing station E, fuser 68 generatessufficient heat to permanently affix the toner powder image to supportmaterial 36. One type of suitable fuser is described in US. Pat. No.3,498,592 issued to Moser et al. in 1970. Support material 36, with thetoner powder image affixed thereto, is, thereupon, advanced by endlessbelt conveyors 70 and 72 to catch tray 74. Catch tray 74 is arranged topermit the machine operator to readily remove the completed copy fromthe printing machine.

The last processing station in the direction of rotation of drum 10, asindicated by arrow 14, is cleaning station F. As heretofore indicated, apreponderance of the toner particles are transferred to support material36, however, some residual toner particles remain on photoconductivesurface 12. At cleaning station F, these residual toner particles areremoved from photoconductive surface 12. The residual toner particlesare inigenerating device (not shown) adapted to neutralize upper surface82a is disposed closely adjacent to the root diameter of the gear teeth.Similarly, gear 44 includes a plurality of resilient portions 84thereon. Resilient portions 84 are arcuate apertures orslots 84 whichextend preferably over an arc of about 52 /,the arc may range from about45 to about 60. In this case,

four slots 84 are shown in gear 44. Each slot 84 is preferably about 1inch in width and has the uppermost surtially brought under theinfluence of a cleaning corona the remaining electrostatic charge ontoner particles and photoconductive surface 12. Thereafter, theneutralized toner particles are cleaned from photoconductive surface 12by rotating fibrous brush 76. Brush 76 is positioned in contact withphotoconductive surface 12. One type of suitable brush cleaning deviceis described in US. Pat. No. 3,590,412 issued to Gerbasi in 1971.

It is believed that the foregoing description is sufficient toillustrate the general operation of a multi-color electrophotographicprinting machine utilizing the teachings of present invention therein.Referring now to FIGS. 2 and 3 for the specific subject matter of thepresent invention, FIG. 2 depicts gear 40 mounted on shaft member 42attached to photoconductive drum l0 and gear 44 mounted on shaft member46 attached to transfer roll 38. As shown in FIG. 2, drive motor 16rotates gear member 48. Coupling 80 connects shaft 46 to shaft 78 whichrotates transfer roll 38 in the direction of arrow 48. Drive motor 16 ismounted in line and coupled directly to the transfer roll shaft 78.Flexible coupling 80, Le. a metal bellows, is provided between transferroll shaft 78 and drive shaft 46. Bellows coupling 80 is preferably madefrom a steel having a torsional stiffness of about 750 inch-pounds/perdegree to prevent image mis-registration. Identical gears 40 and 46 aremounted on the transfer roll shaft 46 and photoconductive drum shaft 42.Preferably, gears 40 and 44 and 48 are tooth plastic gears. Gears 40 and44 preferably have a pitch diameter of 5.73 inches and a circular pitchof 0.375 inches. Drive motor 16 is a synchronous speed motor whichrotates transfer roll 36 in the direction of arrow 48at 9.6 revolutionsper minute. Hence, gears 40 and 44 also'rotate at 9.6 revolutions perminute in the directions of arrows l4and 48, respectively.

Gear 40 includes a plurality of resilient portions 82 (in this casefour) disposed about an arc thereon. Resilient portions 82 are arcuateapertures or slots in gear 40. Slots 82 extend in an arc preferablyranging from about 45 to 60, the preferred are being about 529?. Thewidth of slots 82 preferably is about 1 inch and face 84a thereofclosely adjacent to the root diameter of the gear teeth of gear member44.

In operation, the angular rotation of gear 40 is synchronized with theangular rotation of gear 44. Since both gear 40 and gear 44 rotate atthe sameangular ve locity, i.e. 9.6 revolutions per minute, the contactzone will remain substantially unchanged between each of the gears.Hence, resilient portions 84 on gear 44 is disposed to pass through thecontact zone when rigid portions 86 of gear 40 passes therethrough.Similarly, rigid portions 88 of gear 44 passes through the contact zonewhen resilient portions 82 of gear 40 pass therethrough. Hence, a rigidportion on one of the gears is always aligned with a resilient portionon the other of the gears. In this way, the gear member having theresilient portion passing through the contact zone flexes so as toeliminate backlash or relative movement between each of the gears. Sinceeach of the gears is substantially identical, gear 40 will be discussedin detail, with reference to FIG. 3.

Turning now to FIG. 3, gear 40 is shown therein as including four slots82 thereimGear 40 has 48 teeth and a pitch diameter of 5.73 inches witha circular pitch of 0.375 inches. Each slot 82 preferably extends overan arc of 52%", the arc may range from about to about The width of slot82 is preferably about 1 inch. Each slot 82 is equally spaced about gear40 on substantially equal radii thereon. Rigid portions 86 areinterposed between slots 82. In operation, each slot 82 is adapted to belocated opposed from a rigid portion of the other gear as the two meshedgears pass through the contact zone. In this manner, the gear having theslot passing through the contact zone flexes to eliminate backlashbetween each of the gears. This flexing continues to occur with regardto alternate gears. Initially gear 40 may flex as the slot thereinpasses through the contact zone and subsequently gear 44 may flex as theslot therein passes through the contact .zone. Hence, one of the gearsis continually flexing as its re spective slot passes through thecontact zone. This flexure or deflection of each of the gears on asubstantially continuous basis eliminates backlash and relative movementbetween each of the gears. Hence, it is feasible to utilize a pair ofshaft members having a comparatively loose tolerance between centerswhile substantially eliminating backlash through the use of the gearmembers of the present invention.

In recapitulation, it is evident that the gear members of the presentinvention cooperate with one another to substantially eliminate relativemovement therebetween. This enables the center to center distance of therespective shaft members to be toleranced loosely. Thus, it is feasibleto readily remove the transfer roll and photoconductive drum whilesubstantially eliminating backlash therebetween. In this manner, therequisite image registration between successive toner powder imagestransferred to the sheet of support material is maintained. Thisfacilitates the servicing of a multicolor electrophotographic printingmachine while tives, modifications and variations that fall within the.

spirit and broad scope of the appended claims.

What is claimed is:

1. An apparatus rotating a first shaft member at 'a substantiallypredetermined angular'velocity relative to a second shaft member withsubstantially no relative movement therebetween, including:

a first gear member mounted on the first shaft memher, said first gearmember having a plurality of resilient portions equally spaced betweensubstantially rigid portions at substantially about a preselected radiusthereon; and

a second gear membermounted on the second shaft member and meshing withsaid first gear member in a contact zone, said second gear member havinga plurality of resilient portions equally spaced between substantiallyrigid portions and at substantially about a pre-selected radius thereon,said first gear member being adapted to mesh with said second gearmember such that each of the resilient portions of said first gearmember pass through the contact zone when each of the rigid portions ofsaid second gear member pass therethrough.

2. An apparatus as recited in claim 1, wherein the resilient portions ofsaid first gear member include a plurality of substantially equallyspaced arcuate apertures extending over a preselected arc in the regionof the root diameter of said first gear member.

3. An apparatus as recited in claim 1, wherein the resilient portions ofsaid second gear member include a plurality of substantially equallyspaced arcuate apertures extending over a preselected arc in the regionof the root diameter of said second gear member. a

4. An apparatus as recited in claim 1, wherein said first gear memberand said second gear member are preferably made from a plastic material.

5. An electrophotographic printing machine of the type having aphotoconductive drum mounted on a first shaft member arranged to rotateat a predetermined angular velocity relative to asecond shaft memberhaving a transfer roll mounted thereon, including:

a first gear member mounted on the first shaft member, said first gearmember having a plurality of resilient portions equally spaced betweensubstantially rigid portions at substantially about a preselected radiusthereon;

a second gear member mounted on the second shaft member and meshing withsaid first gear member in a contact zone, said second gear member havinga plurality of resilient portions equally spaced between substantiallyrigid portions at substantially about a pre-selected radius thereon,said first gear member being adapted to mesh with said second gearmember such that each of the resilient portions of said first gearmember pass through the contact zone when each of the rigid portions ofsaid second gear member pass therethrough; and

means for rotating one of the shaft members so that said gear memberassociated therewith drives said gear member associated with the othershaft member, thereby rotating the photoconductive drum and transferroll at the predetermined velocity with substantially no relativemovement therebetween.

6. A printing machine as recited in claim 5, wherein the resilientportions of said first gear member include a plurality of substantiallyequally spaced arcuate apertures extending over a preselected arc in theregion of the root diameter of said first gear member.

7. A printing machine as recited in claim 5, wherein the resilientportions of said second gear member in= clude a plurality ofsubstantially equally spaced arcuate apertures extending over apreselected arc in the region of a root diameter of said second gearmember.

8. A printing machine as recited in claim 5, wherein said first gearmember and said second gear member are, preferably, made from a plasticmaterial.

1. An apparatus rotating a first shaft member at a substantiallypredetermined angular velocity relative to a second shaft member withsubstantially no relative movement therebetween, including: a first gearmember mounted on the first shaft member, said first gear member havinga plurality of resilient portions equally spaced between substantiallyrigid portions at substantially about a pre-selected radius thereon; anda second gear member mounted on the second shaft member and meshing withsaid first gear member in a contact zone, said second gear member havinga plurality of resilient portions equally spaced between substantiallyrigid portions and at substantially about a pre-selected radius thereon,said first gear member being adapted to mesh with said second gearmember such that each of the resilient portions of said first gearmember pass through the contact zone when each of the rigid portions ofsaid second gear member pass therethrough.
 2. An apparatus as recited inclaim 1, wherein the resilient portions of said first gear memberinclude a plurality of substantially equally spaced arcuate aperturesextending over a preselected arc in the region of the root diameter ofsaid first gear member.
 3. An apparatus as recited in claim 1, whereinthe resilient portions of said second gear member include a plurality ofsubstantially equally spaced arcuate apertures extending over apreselected arc in the region of the root diameter of said second gearmember.
 4. An apparatus as recited in claim 1, wherein said first gearmember and said second gear member are pReferably made from a plasticmaterial.
 5. An electrophotographic printing machine of the type havinga photoconductive drum mounted on a first shaft member arranged torotate at a predetermined angular velocity relative to a second shaftmember having a transfer roll mounted thereon, including: a first gearmember mounted on the first shaft member, said first gear member havinga plurality of resilient portions equally spaced between substantiallyrigid portions at substantially about a pre-selected radius thereon; asecond gear member mounted on the second shaft member and meshing withsaid first gear member in a contact zone, said second gear member havinga plurality of resilient portions equally spaced between substantiallyrigid portions at substantially about a pre-selected radius thereon,said first gear member being adapted to mesh with said second gearmember such that each of the resilient portions of said first gearmember pass through the contact zone when each of the rigid portions ofsaid second gear member pass therethrough; and means for rotating one ofthe shaft members so that said gear member associated therewith drivessaid gear member associated with the other shaft member, therebyrotating the photoconductive drum and transfer roll at the predeterminedvelocity with substantially no relative movement therebetween.
 6. Aprinting machine as recited in claim 5, wherein the resilient portionsof said first gear member include a plurality of substantially equallyspaced arcuate apertures extending over a preselected arc in the regionof the root diameter of said first gear member.
 7. A printing machine asrecited in claim 5, wherein the resilient portions of said second gearmember include a plurality of substantially equally spaced arcuateapertures extending over a preselected arc in the region of a rootdiameter of said second gear member.
 8. A printing machine as recited inclaim 5, wherein said first gear member and said second gear member are,preferably, made from a plastic material.